Guys,
Just got my car scanned by the dealership and got the code for the upper cat converter (P0420). I had the VSC VSC off and Engine light come on a few days ago. I had taken a long trip that day to visit the Mercedes Benz Museum and later that night, the lights came on. I've also been experiencing bad gas mileage for about 3+ months, so now I know why this is.

I know the OEM cats for these cars are $928 (carson), which I won't pay, so I was thinking if it was a good idea to just go with headers and call it a day. I also though buying aftermarket cats, which run anywhere from $89 and up.
what do you guys think is the best solution to my problem? Suggestions are welcomed in this thread...

 

For the VSC lights, it's your TPS.. not an easy fix.

Check your O2 sensors for the cats, one or more might be bad. You can always get away with installing CATS from an SC, and mock it up real nice

 

I was there when the mechanic plugged the scanner and it only pulled one code:P0420. I didn't pull the normal codes people are getting for the VSC light. Either way, I would pay these guys to change the TPS if need be, they've been more than generous with me every time I go...no charge for scanning and this is the third time I've gone there for help without charge.

I will check the O2 sensor's just to make sure. Thanks!

 

Update: I replaced the o2 sensor and reset the code, but the lights came back! I'm suspecting the cat is bad. Also, it bought this car from the dealership with 30+K miles on it and I couldn't believe the sensor was JB welded to the manifold. I had to re-tread the tread in order to fit the new one. odd!

I've read numerous threats about this problem, but I still haven't seen someone post an aftermarket Cat they've bought to fix this problem. Can anyone post a website, model, etc...? I know there are a bunch of aftermarket cats out there, but they all vary in size and i don't know, nor I trust websites saying a specific cat will work. I would like to hear it from someone that's done this before, using aftermarket Cat's.

Let me know please.

 

Yea I would like to know about aftermarket cats too for future use... BTW which o2 sensor did you change? Did you read the thread about this on the sticky by chance as well??

 

I had the same problem. If you're under the 8yr/80K emissions warranty (not sure how many miles you have on your 04), you can get them replaced for free at the stealership. My stealership did replace the cats for free. I guess it is a common problem for the 2GS cats to go out early in its life. I thought I just had bad luck lol. Oh well, I guess my luck wasn't too bad, since I had it replaced for free.

If you are under warranty, go to a stealership you like, and they will inspect. Their "workup" with this code goes like this. 1) replace 02 sensors, which you, and at that time, I have already done. 2) replace cats if CEL doesn't go away. GL

 

definitely OEM cat, especially under warranty. I have installed after market cat an it's fine. I've put in my OEM back since my problem was with leaks (did SS headers install)... tightened the bolts and it's gone now.

 

Sam, which aftermarket cats did you buy? I'm getting under the car this weekend to determine if its a leak or not. I hope so!

 

I got mine from wundercarparts off ebay. It's less than 200 bux.

Also, the reason I know it wasn't my cat was because I swapped the left and right cat. The CEL CODE still said the same thing. You can do the same before making an expensive purchase.

 

My brother's MDX just kicked this same code and i'm hoping it's just the o2 sensors.

 

So any update on this as of yet? O2 sensors or did you go with an aftermarket cat?